This invention relates to electrical devices and, more particularly, to electrode structures for thin film devices.
Certain types of materials will emit a narrow wavelength band of radiation as a result of a change in energy states when a sample of the material is excited by an external source of energy. No significant change in the temperature of the material is associated with this phenomenon, which is known as electroluminescence where the luminescence is induced electrically.
One application in which the electroluminescent effect may be used to great advantage is to achieve the video output in a flat panel display system. Such a device can exhibit significant advantages, such as reduced weight and volume, as compared to more conventional cathode ray tube television systems. Furthermore, a flat panel display system is potentially cheaper to produce and can be configured to achieve high reliability under severe operating conditions.
One flat panel display system, for example, has been developed around a miniature active matrix, utilizing a thin film electroluminescent emitter and high density hybrid electronic drivers integrated with the display to produce a miniature video display system. In such a device, a pattern of parallel electrodes is deposited in one direction on a first side of the thin film, and another set of electrodes is applied in an orthogonal direction on a second side of the film. In conjunction, these two sets of electrodes are utilized to provide two dimensional x-y addressing, effectively establishing a matrix of emitter elements. The appropriate elements may then be stimulated to achieve a luminescent picture display.
Some of the properties of an electroluminescent film, however, present difficulties with respect to utilizing such a film to achieve a practical and reliable display device. An electric field applied across such a film can cause sporadic breakdowns of the film at particular locations, which breakdowns can in turn produce a break in the continuity of the overlying electrodes at such locations. When standard electrode deposition techniques are used, for example, these breaks in the electrode can cause the failure of an entire line electrode, resulting in substantial degradation of the image displayed by such a system. Thus, a need has developed for an electrode structure which can be utilized in thin film devices without being subject to failure as a result of point failures in the associated thin film.